Dear Master Gardener: This is the worst year I have had when it comes to deer! I keep spraying — they keep eating — even herbs! What else can we do besides spray deer repellent, which doesn’t seem to be deterring them this year?

Answer: I have been writing this column since 2008 and this summer has brought in the most deer complaints and questions ever! It is so frustrating and sad when your lilies and daylilies are just about to bloom and the deer come along and nip off all the buds. Unfortunately, tall fencing is the only truly foolproof method. It is also unsightly and very inconvenient for maintenance. Fencing is great for vegetable gardens, but who wants fencing around all their flower beds? The year my son and daughter-in-law got married in our yard was another year the deer were relentless. I finally resorted to putting electric fence around flower gardens, then taking it all down the day before the rehearsal dinner. The poor UPS man was afraid to deliver wedding gifts for fear of being electrocuted.

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One type of barrier that has worked for me (and many other local gardeners) for smaller garden areas is using fishing line. String heavy duty fishing line around garden stakes (I use 4- or 5-foot green ones to try to blend in with the surrounding environment). Although some university extensions recommend two strands, I have experimented and found three to be more effective. Put a strand about 18-24 inches off the ground, another strand close to the top of the stakes, and another one half-way between the two. Deer bump into this, are surprised at something they cannot see, and often turn away.

Some gardeners (and I) have found success with motion activated sprinklers. They not only start spraying water everywhere, they also make a noise that scares the deer away.

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Many local gardeners are responding to the heavy deer pressure by loading up on Milorganite. Like many things lately the demand has outpaced the supply, so there is a shortage of Milorganite, too. This product is made by the Milwaukee Metropolitan Sewerage District and is composed of heat-dried microbes that have digested the organic matter in wastewater. It is a slow-release nitrogen fertilizer that is safe to use on all gardens, including vegetable gardens. The smell is not only offensive to humans, but some deer seem to be offended by it also and stay away.

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The University of Minnesota and other universities have done considerable research on deer repellents. Having egg in a repellent seems to be the key ingredient of the most effective repellents. If you are purchasing a commercial deer repellent, look for egg as an ingredient. For thrifty minded gardeners, the U of M has a recipe for DIY deer repellent that has been deemed reliable if applied diligently. There are other online recipes, but gardening folklore isn’t always research-based. U of M research has shown that adding other ingredients may mask the egg odor enough to reduce the effectiveness of an egg spray.

  1. Use a blender to blend three whole eggs thoroughly in water.

  2. Pour the mixture into a container and add water to reach one gallon. Strain.

  3. Spray the mixture onto new growth with thorough coverage using a hand sprayer or tank sprayer for larger amounts. Spray until leaves are wet and have a sheen.

  4. Reapply every two weeks or after rain.

Dear Master Gardener: Can I prune my shrubs, specifically yews, right now?

Answer: It depends on what type of shrubs you are pruning. If you have a hedge, it may be pruned in spring and again in mid-summer to keep it dense and attractive. Spruces can be pruned any time, but it’s probably better to prune them in late winter/early spring. Arborvitae, junipers, yews, and hemlocks can be pruned any time until the middle of summer. Shrubs that bloom early in the growing season on last year’s growth, such as azalea, chokeberry, chokecherry, forsythia, lilac, and early blooming spirea, should be pruned immediately after they finish blooming. Shrubs grown primarily for their foliage rather than their flowers, such as ninebark, alpine currant, burning bush, dogwood, and honeysuckle, should be pruned in spring before growth begins.

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Dear Master Gardener: Has all this extremely hot weather brought out more insect pests?

Answer: Certain insects thrive in hot weather. Aphids, thrips and spider mites are the insects that thrive in hot weather like we have been experiencing. The heat allows them to produce more offspring in less time. Aphids in particular love heat and, unlike most insects, give live birth. In addition, the females produce offspring without mating, giving live birth to genetic clones of themselves, which allows them to grow their populations quickly. If you find a sticky substance on your plant’s leaves and fruit, you probably have aphids. Unfortunately, aphids also transmit diseases when they feed on a virus-infected plant then move to an uninfected plant to feed. Thrips feast on juicy, well-watered plants during hot weather. Like aphids, they also reproduce quickly. Lastly, spider mites usually feed on the undersides of leaves and can turn leaves and evergreen needles brown and crispy. They overtook an arborvitae in my garden last year, eventually killing it. They too reproduce quickly in hot conditions, so their populations are most likely exploding in gardens right now.

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The first inclination gardeners tend to have with these pests is to reach for an insecticide, but this is rarely a good solution. Many pesticides are not selective in what they kill and often kill beneficial insects and pollinators. The best, and most environmentally friendly, way to rid your gardens of these three pests is by knocking them off the leaves (don’t forget the undersides) with a blast of water from your hose. They are usually killed by the blast. The least toxic chemical control method for soft bodied insects is insecticidal soap (not dish soap). You have to make sure that the insects come in direct contact with the soap, so it is important to spray both the top and undersides of the leaves. According to Oregon State Extension, commercial formulations of insecticidal soaps have been extensively tested on plants, so they are safer than homemade solutions. The good news is that once this heat wave ends, these insect populations are often reduced.

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You may get your garden questions answered by calling the new Master Gardener Help Line at 218-824-1068 and leaving a message. A master gardener will return your call. Or, emailing me at umnmastergardener@gmail.com and I will answer you in the column if space allows.
University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. Information given in this column is based on university research.